The Mont Blanc Tunnel linking France and Italy is opened.

After 19 years of planning and construction, the Mont Blanc Tunnel officially opens. The new tunnel stretches 7 miles, linking the French town of Chamonix and the Italian town of Courmayeur. Buried 1.5 miles under the Alps’ highest peak, it becomes the world’s deepest road tunnel beneath rock and gains infamy after a deadly 1999 fire.

Until the opening of the tunnel, road traffic in the Alps between France and Italy wended its way over hairpin turns and sharp grades, with mountain passes closed the majority of the year because of snow. Italian construction teams began drilling a tunnel into Mont Blanc (or Monte Bianco on their side) to build a year-round route in 1946. The next year, France and Italy signed an agreement to build the tunnel together.

Construction, however, did not begin in earnest until May 30, 1959, with the help of an 82-ton tunnel-boring machine. Tunneling began at 4,091 feet on the French side and at 4,530 feet on the Italian side.

It took 783 tons of explosives to complete the drilling. The French and Italian teams met Aug. 4, 1962, with a discrepancy of only 5.12 inches between the two sides.

When it opened in a ceremony featuring Presidents Charles De Gaulle of France and Giuseppe Saragat of Italy, the Mont Blanc Tunnel became the world’s longest highway tunnel, more than three times longer than the previous recordholder, Liverpool’s Mersey Tunnel.